Pressure generating device



July 8, 1969 I N, o, mu 3,453,687

PRESSURE GENERAT ING DEVIC E Filed Sept. 28; 1966 Sheet 1 of 4 I TXi''7w @9 I J hyermior Niel; 0. .Yo W% July 8, 1969 N. o. YOUNG 3,453,687

PRESSURE GENERATING DEVICE Filed Sept. 28, 1966 Sheet of 4 N. O. YOUNGPRESSURE GENERATING DEVICE July 8, 1969 Sheet 3 M4 Fil gd Sept. 28. 1966July 8, 1 969 N. o. YOUNG 3,453,637

I PRESSURE GENERATING DEVICE Fild Sept. 28, 1966 Sheet 4 of 4 us. or.1s--s United States Patent 3,453,687 PRESSURE GENERATING DEVICE Niels 0.Young, Lincoln, Mass., assignor to Block Engineering, Inc., Cambridge,Mass., a corporation of Delaware Filed Sept. 28, 1966, Ser. No. 582,648Int. Cl. B29c 17/00 Claims ABSTRACT OF THE DISCLOSURE Strip means arecoiled in several turns around an object or pressure transmitting core.The strip windings slide freely upon themselves and are forciblytightened around the object by differential movement of the inner andouter strip ends. A single strip, or interleaved strips, or stripsoppositely wound side by side can be used.

The field of the present invention relates to pressure generatingdevices, and more particularly, but not ex clusively, to devices forgenerating ultrahigh pressures.

At present, the devices utilized for generating extremely high pressuresare unwieldy. Most of these devices employ hydraulic machinery to exertpressure, and therefore require pumps and a large and heavy frame tomount the hydraulic components. Another notable disadvantage of thepresent hydraulic equipment is the time per working cycle required,which is determined in part by the hydraulic pump capacity.

Objects of the present invention are to provide a device for generatingextremely high pressures which requires no hydraulic machinery, whichrequires neither a heavy nor a large frame, which can be constructedcompactly and inexpensively, which has a short working cycle duration,which can be easily adapted to generate low as well as very highpressures.

The substance of the invention may be shortly stated as contemplatingbroadly, the generating of pressure on an object by coiling strip meansin a multiplicity of windings around the object with freedom of thestrip means to slide upon itself, and by forcibly tightening the stripmeans around the object by relative movement of the inner and outer endsof the strip means. Preferably, a core member that presents acompressible effectively cylindrical surface is interposed between thestrips and the object.

In a practically important particular aspect, the invention utilizes apair of strips oppositely wound, side by side, on an effectivelycylindrical core surface. The strips are forcibly tightened around thecore by a harmonic drive of known principle which moves the outer endsof the strips in opposite directions, and which thereby causes the coreto shrink and to generate pressure on an object within the core.

In another aspect, the invention contemplates two strip means wound inan interleaving fashion about a core member.

Whether the strips are arranged side by side or interleaved, either theouter ends can be held fixed with the inner ends attached to the corewhich is rotated by drive means to tighten the strip, or the core can befixed and the outer strip ends pulled. Also, movement can be applieddifferentially to both the outer ends of the strips and their inner endson the core.

These and other objects and aspects of the novel substance will appearfrom the following theoretical explanation and detailed description ofseveral practical embodiments of the invention.

The description refers to a drawing in which FIGS. 1 to 3 are schematicviews presented for the purpose of explaining the theory of operation ofthe invention;

FIG. 4 is an axial cross-section of one practical embodiment of theinvention, as on line 44 of FIG. 5;

FIG. 5 is a section on line 55 of FIG. 4;

FIG. 6 is a radially directed view of a portion of the harmonic drivemeans employed in the embodiment according to FIGS. 4 and 5;

FIG. 7 is a side view of the device according to FIGS. 4 to 6;

FIG. 8 is a partial sectional view on line 8-8 of FIG.

FIG. 9 is a schematic view of a second embodiment of the invention;

FIG. 10 is an axonometric view of a core assembly used in the embodimentaccording to FIG. 9;

FIG. 11 is an end view of the core assembly shown in FIG. 10;

FIG. 12 is a side view of the core assembly of FIG. 10 showing the drivemeans therefor in section; and

FIG. 13 is a side view of the drive means for the embodiment accordingto FIGS. 9 to 12.

The theory on which the construction and operation of the hereindescribed embodiments of the pressure device according to the inventionare based, will first be explaind with reference to FIGS. 1 to 3. InFIG. 1, a cylindrical core C of radius r is fixed against rotation, asschematically indicated by a transverse key and groove guide G. Spirallywound on the core is a strip S of uniform width w and thickness t. Theoutside radius of the coil is r and its inside radius is r the same asthe radius of the core. The innermost end of the strip is fixed to thecore, and the outer free end of the strip is pulled at a tension T Thecoiled strip is lubricated so that it slides easily upon itself.Lubricants providing a coefficient of friction below 0.05 are readlyobtainable, and therefore, in the following analysis, the effects offriction will be ignored. A rigorous analysis including the effects offriction has been undertaken; it indicates that the following simplifiedanalysis yields results accurate to within a few percent forcoefiicients of friction on the order of 0.05 and below.

The strip is coiled into a spiral that is described, in polarcoordinates, by

t r= 0+r for r grgr The stress in the strip is given by S T W1 To findthe pressure generated by the coiled strip, we first calculate theradial pressure increment across each strip caused by the tension in thestrip. Referring to FIG. 2 which represents a generalized strip portionof an incremental angle A0, the tension T in the strip resolves into aradial force F which is given by F:T sin A0 This force acts over an areaA given by A=wrA6=(A0) Wt/41r' The incremental pressure change A in aradial increment t is then given by Ap/t=lim(A6 0)F/tA or, uponperforming the indicated operations, by

Ap/t=T/wrt=S/r Because i is very small as compared to r, the expressionAp/t may be replaced by dp/dr. Therefore dp/dr=S/r wherein, as above, S:T /wt, the stress in the strip.

Ignoring the effects of friction, the tension T with in the strip is aconstant equal to the tension T at the free end of the strip. Becausethe strip has constant dimensions t and w, the stress S is also aconstant, equal to the stress S at the free end of the strip. Thepressure developed at any radius r is then given by The above expressioncan be used to find the optimal sample volume, or the largest availablespace in which to place a sample, for a given coil size, a given stressin the strip, and a given pressure desired on the sample. The coiledstrip of outer radius r and inner radius r en compasses for practicalpurposes, instead of the core C, a vise or anvil assembly as shown inFIG. 3. This assembly has an outside radius corresponding to r of FIGS.1 and 2, and a cylindrical sample space of radius r The pressure P atthe vise jaws (at radius r,,) is related to the pressure P generated bythe coiled strip at radius r by the expression:

a c( a) where P =S ln(r,,/r

For given values of P S and r the maximum radius r,,, and the maximumsample volume can be derived by finding dr /dr and equating it to zero.In this manner it is found that the maximum value of r, occurs when or r/r =e=2.7l8. The optimum value of r is then r =r S e1 The sample volumeV is given by V w1rr w1rr S /e P It will be noted that the sample volumevaries with the square of the working stress S Hence, if the strip isworked at a high stress, the equipment size can be kept down. Becausethe strip is made of thin material, it can develop high strength, andconsequently a significant saving in space and weight over conventionalram-type equipment can be realized in the coil press according to theinvention.

In terms of equipment weight M, which is proportional to r w, the aboverelation for V becomes where K 1r/pe with p the density of the coilmaterial, for example 7.9 g./ml. of cold rolled steel. The inequalityexpresses the fact that the press as a whole includes other than coilmaterial and that the sample volume V is not corrected for gasket andsimilar volume, nor for vise efliciency.

By way of example, it may be assumed that a steel strip S withdimensions w=50 mm. and t=.l6 mm. is wrapped several times around a coreor vise structure with r =25 mm. and lubricated with molybdenumdisulfide which has a coefficient of friction of less than 0.05. At apressure P =7OK bar and S =25 kg./ sq. cm. ths results in a V /M valueof .502 minimum possible metric tons of coil per liter of sample.Further assuming that frame, power supply, and other auxiliaries aretwice the coil weight, that the pressure efficiency at 70K bar is /2,and that the sample occupies about one quarter of the vise jaw gap, theV /M ratio decreases by a factor of about 16. At the assumed pressure of70 kilobars, the equipment will weigh about 12 tons/ liter at S =25 kg./sq. cm. strip stress which is appreciably lighter than heretoforeavailable press equipment for similar purposes. Test results to the sameeifect derived from a practical embodiment will be given below withreference to the detailed description of that embodiment.

Referring now to FIGS. 4 to 8, an embodiment of the invention designedto generate ultrahigh pressures will be described. In this embodiment,two strips 10a and 10b of high tensile strength material are utilized.Except for their innermost and outermost wraps, the two strips arelubricated with a lubricant providing a low coefficient of friction suchas molybdenum disulfide, and are spirally wound in opposite directionson a core member 12 having an effectively cylindrical outer surface, theunlubricated innermost wraps of each strip 'frictionally engaging thisouter surface. The strips are prevented from sliding axially by a washer14 which separates the strips, and by end caps 16a and 16b which abutthe strips at their outer edges.

As shown in FIG. 5, the core member 12 comprises an inner shoe 12.1 andan outer shoe 12.2 partially surrounding the inner shoe. The inner andouter shoes each have mating crescent shaped cross sections which permitthe core member to maintain an effectively cylindrical inner and outersurface as it shrinks when pressure is applied to it. To keep the innerand outer shoes in cylindrical disposition, that is from rotating withrespect to each other, the shoes are provided at their ends with axiallyextending bosses 18 which are constrained to move only in radialdirections by radial slots 20 provided in the end caps 16a and 16b.

Spaced within the core member 12 is a plurality of, here four, anvils 22of shape identical to each other for transmitting pressure from the coremember with its shoes to a location central among the anvils. Each anvil22 extends between the end caps 16a and 16b and is a cylindrical sectortruncated to provide a central space 24. Plugs 26a and 26b recessed inend caps 16a and 16b close off the ends of the space 24 within the anvilassembly. The object upon which pressure is desired (not shown) isenclosed in a gasket (not shown) of lava or other suitable material, andit is placed in the space 24. If desired, instruments or sensing devicescan be enclosed with the object, and their leads or indicators passedthrough ports 28 provided in the end caps 16a and 16b.

For tightening the anvil assembly, the outer ends of the strips 10a and10b are moved relatively to their inner ends by drive rings 30a and 30bwhich are seated for rotation in annular frame members 32a and 32brespectively. The drive rings are coupled to the outermost wrap of eachstrip by clutch means 34a and 34b, each of which comprises an outer setof four curved Wedges 36a, 36b, respectively, secured to the drive ringsby bolts 38a and 38b and an inner set of four curved overlapping wedges40a, 40b which slidably engage the outer wedges 36 on one side, andwhich frictionally engage on the other side the outermost wraps of thestrips 10a and 10b. As shown in FIG. 5, the outer wedges 36 areuniformly spaced about the respective drive ring and have their narrowends pointing in the direction in which the outer end of the strip ismoved for tightening (here counterclockwise); the inner wedges 40 aredisposed with their narrow ends pointing in the opposite direction.Thus, rotation of a drive ring, such as 30b, in a direction which willtighten the strip (counterclockwise in FIG. 5) Will cause the innerwedges 40 to slide upon the outer wedges 36 which will thereby cause theinner wedges 40 to remain in contact with the outer wrap of theshrinking coiled strip 10b. Conversely, as the drive ring is moved in adirection to loosen the strip, the inner wedges 40 will slide so as toremain in contact with the expanding strip 10b. This arrangement assuresthat the forces on the outer wraps of the strips will be uniform andwill be substantially tangential with no unbalanced radial componentwhich would tend to displace the core member 12.

To assure that the inner wedges 40 will move synchronously and remainuniformly spaced, each is provided with an axially extending boss 42.The bosses 42 fit into radial slots 44 provided in rotatablesynchronizing rings 46a and 46b mounted in the frame members 32a and 32brespectively. The synchronizing rings 46a and 46b, together withportions of the drive rings 30a and 30b, also serve as axial guides toprevent the inner wedges 40 from sliding axially, although they have toslide on each other peripherally. The synchronizing rings are furtherprovided with flanges 461a and 46.1b which receive and center the endcaps 16a and 16b.

To tighten the strips a and 10b and thereby generate pressure, the drivering-s 30a and 30b must be rotated in opposite directions. The drivemeans which accomplishes this will now be described.

Secured to the drive rings 30a and 30b by means of pins 50 (FIGS. 4, 6)is a pair of harmonically meshing face gears 52 and 54. The face gears52 and 54 have different numbers of teeth; thus the gears can mesh onlyat a limited number of peripheral sectional regions. For example, if oneof the gears has 300 teeth and the other of the gears has 297 teeth, thegears will be relatively positioned to mesh in but three equally spacedpositions or sector regions.

By providing means for holding the gears in meshing engagement in atleast one of these regions, and further providing means for rotating theholding means circumferentially of the gears, so that the region ofmeshing engagement moves, it is apparent that the gears will rotaterelatively to one another in opposite directions. For each revolution ofthe region of meshing engagement, gears having 300 and 297 teeth, forexample, will rotate ,4 revolution with respect to each other inopposite directions. This harmonic drive system is thus well suited forthe purpose of moving the drive rings 30a and 30b in opposite directionsto tighten strips 10a and 10b about the core 12.

The face gears 52 and 54 each have an inner portion secured by the pins50' to the drive rings 30a, 30b, and in sliding engagement with oneanother; an outer portion upon which the teeth are cut; and a thinnerand therefore flexing central portion 'between the inner and outerportions. Preferably, the teeth on the outer portions are cut slightlyconically, so that the teeth will mesh along their entire length whenthe gears are flexed inwardly into meshing engagement, as shown at thebottom of FIG. 4. To minimize the amount of flexing that takes place inthe central flexing portion of the gears, it is preferable to axiallylocate the teeth such that they are in half-meshing engagement when thegears are in their unflexed state. That is, the teeth are cut such thatthe gears flex inwardly and outwardly in equal amounts when changingfrom a completely meshing engagement to a completely nonmeshingengagement.

The face gears 52 and 54 are guided into and out of meshing engagementby a pair of cam strips 56a and 56b (FIGS. 4, 6) which are mounted incircular slots provided in annular cam strip supports 58a and 58b. Thecam strip supports are, in turn, secured to and move with, a rim member60 upon which there is cut a ring gear 62. The cam strip supports 56aand 56b and the rim 60 are provided with interfitting shoulders toprevent axial movement of the cam strip supports. Because of theseinterfitting shoulders, when assembling the device, it is necessary toreduce the diameter of the cam strip supports 58a and 58b. This isaccomplished by removing a portion 581a or 582a from each cam stripsupport, bringing the free ends together, to reduce the diameter,inserting the cam strip support in the rim 60, and then replacing theportion 58.1a or 58.1b.

The cam strips 56a and 56b each have lobes to correspond to the regionsin which the face gears 52 and 54 will mesh, and they are fixed in thecam strip supports so that these lobes are directly opposed. The camstrips 56a and 56b operate through a bearing assembly comprising outerraces 64a and 64b, roller bearings 66 in retainers 68a and 68b, andinner races 70a and 70b, to force the face gears into meshing engagementin equally spaced regions. At points midway between these regions,

the cam strips permit the teeth on the face gears to be completely outof mesh. The cam strips are shaped so as to hold the face gears inpartially meshing engagement during the transition intermediate thesecompletely meshing and completely unmeshing regions. As shown in FIG. 5,the cam strips may be formed in several segments, the ends of whichoverlap, and are bent, in holes 72 provided in the cam strip supports58a and 58b.

As shown in FIG. 4, the drive rings 30a and 30b are provided with ledgeswhich support retainers 68a and 68b, and race-holders 74a and 74b whichin turn support inner races 70a and 70b. The race-holders 74a and 74bare chamfered to provide clearance for the roller bearings 66. The outerraces 64a and 64b are supported by the rim 60.

The assembly constituted by the rim 60 and cam strip supports 58a and58b, is separated from the drive rings 30b or 30a by a bearing strip 76of Teflon or similar material. It should be noted that where the facegears have two or more positions of meshing engagement, this assembly islargely self-aligning because of the axial stiffeners of the face gearswhen they are in meshing engagement (FIG. 4, bottom). Therefore, onlyone bearing strip, such as 76, need be used.

The rim 60, to which the cam strips 56a and 56b are fastened by means ofcam strip supports 58a and 58b, is provided with a ring gear 62 aspreviously explained. The ring gear 62 is coupled to a reversible motor80 by means of the apparatus shown in FIGS. 7 and 8. As shown in thesefigures, the annular frame members 32a and 32b are provided withintegral radial ears 32.1a and 32.1b on opposite sides thereof. One pairof cars 32.1a and 32.112 has a trunnion 82 secured therebetween; theother pair of ears has a trunnion 84 secured therebetween. Thesetrunnions support the press on a base 86, and one of the trunnions, suchas 84, contains means for coupling the ring gear 62 with the motor 80.As shown in FIGS. 4 and 8, the ring gear 62 is coupled to the motor 80by a pinion gear 88 mounted for rotation in the trunnion 84 and meshingwith the ring gear 62, and a first bevel gear 90 coaxially secured tothe pinion gear 88, and meshing with a second bevel gear 92 transverselymounted for rotation in the trunnion 84 on a shaft 94. The shaft 94 isconnected to motor 80 by a coupling 96.

As shown in FIGS. 4 and 7, the device is encased by two half shells 98and 100 which interfiit with end caps 16a and 16b and which are joinedtogether with bolts (not shown). The shells 98 and 100, together withthe end caps 16a and 16b, form a protective housing for the device toinsure its safe use.

The device shown in FIGS. 4 to 8 operates as follows: The desired sampleis placed centrally among the anvils 22 and the space 24. The device isassembled as shown, with leads for electrical instruments, if desired,passing through ports such as 28 provided in end caps 16a and 16b. Themotor 80, regulated by a rheostat, for example, is turned on and theshaft 94 is rotated. This causes the ring gear 62 to rotate and causesthe cam strips 56a, 56b to move circumferentially around the face gears52, 54. As the meshing regions of the gears 52, 54 moves, the face gearsrotate relatively to one another in opposite directions because of theirdifferent numbers of teeth. Since the gears may move together relativelyto the cam strips, it is apparent that this drive mechanism has adifferential effect. For example, if the strip 10a were initially woundmore tightly than the strip 10b, the gear 52 Would tend to remainstationary with respect to the core while the gear 54 moved relativelyto the gear 52 and the core until the differences in tension weresubstantially eliminated. After the tensions have been equalized, thetwo gears will move relatively to the core equally in oppositedirections.

As the gears 52, 54 move, they carry the drive rings 30a, 30b along withthem. The outer set of wedges 36, attached to the drive rings 30a, 30b,urges the inner set of wedges 40 into contact with the strips 10a and10b.

The outer wrap of each of the strips is pulled in a tangential directionthereby putting the strip under a tension, and causing pressure to begenerated on the core member 12 as hereinbefore explained. As the coremember shrinks, the anvils 22 move inwardly to exert pressure on thesample placed thereinbetween.

The embodiment of FIGS. 4 to 8 has been experimentally tested withfavorable results. Characteristic results for certain test conditionswere obtained as follows:

The strip material used was full hard rolled AISI/ 301 stainless steel1.995/1.998 wide and 0.010 thick with a very smooth surface finish. Eachstrip 10a and 106 was lubricated by using a metal squeegee to apply acreamy suspension of tungsten diselenide in castor oil. Each coilmeasured 2.00" ID. by 5.60" CD. at the time it was installed over thecore member 12 and inside the clutch means 34a and 34b. The number ofwraps was approximately 160-180. The lubricant film at the time ofinsertion was estimated to be less than 0.001" thick.

The pressure gage, inserted directly within the core member 12, had anCD. of 1.75" and a bore of 0.375". This thick-walled tube, by shrinkingunder pressure, exuded water into a burrette one end of which was opento ambient air. The burrette was calibrated to read the pressure on theoutside of the thick-walled tube. This calibration was obtained knowingthe mechanical properties of the thick-walled tube and calculating thevolume of water displaced as a function of pressure.

A revolution counter was connected to the rim member 60 so that theangular displacement of the coils could be monitored, using, if desired,the known gear ratio between the ring gear 62 on the rim and the facegears, in this case 100:1. Thus 100 turns registered by the countercorresponds to one half turn of each face gear or one turn of the facegears with respect to each other.

A continuous measure of the torque applied by the drive motor 80 wasobtained as a measure of the armature current of the compound-wounddrive motor. The armature current registered on an ammeter which wascalibrated to read inch-lb. of torque directly. The motor turned at641:1 with respect to differential coil turns.

Using this experimental test apparatus, the coil press was used forrepetitive pressure generation to over 35 tons/sq. meter on the samplevolume of 165 cubic cms. constituted by the pressure gage. It was foundthat pressure build up was largely uniform, with minor backlash due tostick-slip and extrusion of lubricant being observed. Pressure build upwas rapid as well, a valve in excess of 35 tons/sq. meter being obtainedin less than three minutes. During little more than two turns of theface gears with respect to each other, the observed pressure increasedfrom zero to more than 35 tons/ sq. meter, at which point the inputtorque registered 15.5 cm.-kg. The coil press did not unwind itself as aclock-spring would, as there was sufficient friction between the wrapsto maintain high values of pressure on the gage. However, the stripsreadily unwound to reduce pressure upon application of power, showingthat the press can be used to carry out a completely controlled pressurecycle.

Referring now to FIGS. 9 through 13, another embodiment of the inventionwill now be described. In this embodiment, two strips 200, 201 are woundin an interleaved manner around a core member 202. The outer ends of thestrips 200, 201 are held fixedly in place, as is symbolicallyrepresented in FIG. 9. The core member about which the strips arewrapped comprises two or more anvils 202.1. Each anvil 202.1 has acylindrical outer surface 203 and a flat step 204 on its inner surface.Loosely engaging the flat steps 204 of the anvils 202.1 is a key 205.The key 205 is secured to a gear 206 driven by a second gear 207 whichis attached to a motor (not shown). If desired, the anvils may be drivenby keys inserted at both ends, or in one of the anvils there may beloosely inserted a spacer 208 (FIG. 12) to prevent the anvils fromtwisting.

This second embodiment operates as follows: An object upon whichpressure is desired is placed between the anvils 202.1. The spacer 208and key 205 are inserted between the steps 204 of the anvils. The key205 is rotated in the direction such as to tighten the strips 200 and201. As previously explained, the tension in the strip creates apressure on the core member (here the anvils 202), causing them to moveinwardly to exert pressure on the object.

It will now be understood that instead of holding one end of a strip andmoving the other, a force differential can be applied with equal orunequal strip end excursions effective in opposite senses, or unequalexcursions effective in the same sense.

I claim:

1. A device for generating pressure on an object, comprising:

strip means wrapped in a multiplicity of superimposed windings aroundthe object with freedom to slide upon itself; and

means for forcibly tightening the strip means around the object byrelative movement of the inner and outer ends of the strip means,thereby generating pressure upon the object.

2. A device according to claim 1 wherein the strip means comprises apair of adjacent strips each having freedom to slide upon itself.

3. A device according to claim 1 wherein the tightening means comprises:

a core member interposed between the object and the strip means, thecore member having an effectively cylindrical shrinkable surface withthe inner end of the strip means attached to the surface; and

means for relatively moving the core member and the outer end of thestrip means, thereby causing the surface of the core member to shrinkand thereby generating pressure on the object within the core member.

4. A device according to claim 3 further comprising anvil meansinterposed between the core member and the object for transmittingpressure from the core member to the object.

5. A device according to claim 3 wherein the core member comprises:

an outer shoe having a crescent shaped cross section;

an inner shoe having a crescent shaped cross section disposed partiallywithin the outer shoe to form therewith an effectively cylindrical outersurface; and

means for synchronously holding the inner and outer shoes in thecylindrical disposition of the outer surface.

6. A device according to claim 5 wherein the strip moving meanscomprises:

a pair of coaxial harmonically meshing face gears having differentnumbers of teeth on essentially equal gear radii, whereby the gears canmesh at periodically located peripheral regions;

means for coupling each gear to an outer end of a respective strip;

means for holding the gears in meshing relationship in at least one ofthe periodically located regions; and

means for moving the holding means circumferentially of the gears,thereby moving the regions of meshing engagement and moving the gearsrelatively to each other in opposite directions to tighten the stripsabout the core.

7. A device according to claim 6 wherein the gear and strip couplingmeans comprises:

a drive ring secured to the gear and coaxially surrounding the strip;

an outer set of curved wedges secured to the drive ring in uniformlyspaced relationship and with their narrow ends pointing in thetightening direction of the outer end;

an inner set of curved Wedges engaging the outer end of the strip on oneside and slidably engaging the other side of the outer set of wedges,the inner set of wedges pointing with their narrow ends oppositely tothe direction of the outer set, the inner set of Wedges being uniformlyspaced so as to form a substantially cylindrical inner surface; wherebyas the drive ring is turned the inner wedges slide to adjust thevariations in the size of the coiled strip; and synchronizing means formaintaining the inner set of wedges in uniformly spaced relationship. 8.A device according to claim 1 wherein the strip means includes a pair ofadjacent strips wound in opposite directions around the objects; and thetightening means includes a core member interposed between the objectand the strips, and core member presenting a compressible effectivelycylindrical surface with the inner ends of the strips attached thereto;and means for moving the outer ends of each of the strips relatively tothe respective inner ends. 9. A device according to claim 1 wherein thestrip means comprises a plurality of interleaved strips each havingfreedom to slide upon adjacent strips.

References Cited UNITED STATES PATENTS Kurlfinke l00212 X Price 18-6Edwards 100212 Mc Candlish et al. 100-212 Rappsaet 18-6 X White et al100-212 Kolodin 100-212 Moog.

WILLIAM J. STEPHENSON, Primary Examiner.

US. Cl. X.R.

